The effects of salinity at 50 mm NaCl on floral characteristics, yield comp
onents, and biochemical and physiological attributes of the sensitive rice
variety IR-28 were studied under controlled conditions to determine the cau
ses of sterility in seed set under salinity stress. The results showed sign
ificant decreases in panicle weight, panicle length, primary branches/panic
le, filled seeds/panicle, unfilled seeds/panicle, filled seeds/plant, unfil
led seeds/plant, total seeds/panicle, total seed weight/panicle, 1000-seed
weight and total seed weight/plant. The sodium content in different leaves
and floral parts increased significantly. In contrast, the potassium conten
t was decreased significantly in leaves and floral parts. A reduction in ch
lorophyll a and b was also noted in different parts of the leaves. Inhibiti
on of transpiration and photosynthesis was observed in flag leaves at the g
rain-filling stage. Soluble carbohydrates in different leaves were reduced
significantly in salinized plants but their content in different floral par
ts was increased, with the exception of primary and secondary branch spikel
ets. Under salinity stress, total protein concentration in flag, second and
third leaves were higher than in control plants. The viability of rice pol
len was reduced significantly in salinized plants. It was further observed
that starch synthetase activity (alpha1-4-glucan glucosyle transferases) in
developing rice grains was inhibited very significantly under salinity str
ess. From these results, it is inferred that sterility and significant redu
ctions in seed set in rice were not merely due to reduction or inhibition o
f different biochemical constituents and physiological functions, but were
mainly due to limitation of soluble carbohydrate translocation in primary a
nd secondary spikelets, accumulation of more sodium and less potassium in a
ll the floral parts, and highly significant inhibition of specific activity
of starch synthetase in developing rice grains, thus resulting in failure
of seed set.